1. Field of the Invention
The present invention relates to a driving system for a stepping motor, and more particularly, it relates to a stepping motor driving system suitable to rotate the stepping motor such as a stepping motor for feeding recording paper and/or original in facsimile and the like, by a predetermined steps with uneven cycles.
2. Related Background Art
Generally, in a facsimile and the like, upon transmission, an original is read along a main scanning direction per one scanning line by means of a one line image sensor fixed to the facsimile while feeding the original in an auxiliary direction perpendicular to the main scanning direction. And, upon reception, an image is recorded along a direction perpendicular to a feeding direction of a recording paper per one scanning line by means of a one line recording head fixed to the facsimile while feeding the recording paper. Since the feeding of the original and/or recording paper must be effected with high accuracy and the original must be intermittently scanned in the facsimile system, a stepping motor is generally used for feeding the original and recording paper. As a method for energizing coils of such stepping motor, one-phase-on drive (1-phase energization drive), two-phase-on drive (2-phase energization drive) or half-step drive (1-2 phase energization drive) has been already known; however, because of its ability to provide fine control and high maximum operating frequency, the half-step drive (1-2 phase energization drive) has been adopted to drive the stepping motor for feeding the paper in the facsimile system. It is also known that recording and reading density can be varied in the auxiliary direction during recording and reading operations in facsimile systems, (in the auxiliary direction) by providing a super fine mode of 15.4 line/mm, a fine mode of a 7.7 line/mm or reference a mode of 3.85 line/mm. If the amount of feeding in each auxiliary scanning line at the super fine mode (15.4 line/mm) corresponds to one step of a 1-2 phase energization (half-step drive) for a stepping motor, when the recording paper is fed in the auxiliary direction with one line by the 1-2 phase energization (half-step drive) at other modes, the stepping motor must be rotated by a plurality of steps. Further, the stepping motor should be rotated by a plurality of steps per each motor driving trigger also when the recording paper is cut at each page.
When the stepping motor is rotated by a plurality of steps, it is not reasonably determined whether the first or initial driving of the stepping motor should be started from one phase or two phases, since the present position of phases of the stepping motor differs or varies in accordance with the previous number of steps by which the stepping motor was rotated.
For this reason, in the past, a technique has been proposed according to which energization controls are successively effected in a predetermined order by selecting the order of energizations to reduce noise in consideration of the kind of the driving. Such techniques is disclosed in Japanese Patent Application Laid-Open No. 60-82097.
However, fact whether the driving of the stepping motor at the 1-2 phase energization is started from the one phase or two phases depends upon not only noise but also on other factors.
Explaining with more detail, FIG. 1A shows a step response of a stepping motor in a condition that energization of two phases is changed to energization of one phase at the 2-1 phase-on drive of the motor, and FIG. 1B shows a step response of the motor in a condition that energization of one phase is changed to energization of two phases at the 1-2 phase energization drive (half-step drive) of the motor. FIG. 1A shows the relation between rotation of the rotor of the motor and to residual vibration when the motor is rotated by one step by energization of one phase from a condition by which the stepping motor having a minimum stepping angle of 3.75.degree. was held at energization of two phases. Similarly, FIG. 1B shows the relation between rotation of the rotor of the same rotor and its residual vibration when the motor, which was held at energization of one phase, is changed to energization of two phases. In these Figures, the abscissa indicates time (t) and the ordinate indicates angle of rotation of the rotor (deg). Incidentally, here, it is assumed that a value of winding current per phase flowing at each phase energization is constant.
As apparent from FIGS. 1A and 1B, when the driving of the motor is started from energization of one phase as shown in FIG. 1A, although the building-up of the motor is slower and it takes a longer time to start the rotation of the motor, the amplitude of residual vibration is smaller and the duration of such vibration will also is shorter, than in the case the drive is started from energization of two phases. The delay in the building-up of the motor will be more notable when the motor is stopped or when the motor damping in the reverse direction is great. In order to hasten or quicken the building-up of the motor at energization of one phase, larger energy (energization current) is required. On the other hand, when the driving of the motor is started from energization of two phases (FIG. 1B), although the building-up of the motor is faster, the amplitude of the residual vibration will be greater and the duration of such vibration will also be longer.
For these reasons, if it is desired to apply enough energization current to the motor build up the motor by energization of one phase as shown in FIG. 1A, start energy for the rotation of the motor will be excessive relative to when the motor is built up at the energization of two phases as shown in FIG. 1B. Thus, a problem that arises in vibration noise and motor damping occur.